Biology:Somatostatin

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Short description: Peptide hormone that regulates the endocrine system


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example


Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or by several other names, is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones. Somatostatin inhibits insulin and glucagon secretion.[1][2]

Somatostatin has two active forms produced by the alternative cleavage of a single preproprotein: one consisting of 14 amino acids (shown in infobox to right), the other consisting of 28 amino acids.[3][4]

Among the vertebrates, there exist six different somatostatin genes that have been named SS1, SS2, SS3, SS4, SS5 and SS6.[5] Zebrafish have all six.[5] The six different genes, along with the five different somatostatin receptors, allow somatostatin to possess a large range of functions.[6] Humans have only one somatostatin gene, SST.[7][8][9]

Nomenclature

Synonyms of "somatostatin" include:[citation needed]

  • growth hormone–inhibiting hormone (GHIH)
  • growth hormone release–inhibiting hormone (GHRIH)
  • somatotropin release–inhibiting factor (SRIF)
  • somatotropin release–inhibiting hormone (SRIH)

Production

Digestive system

Somatostatin is secreted by delta cells at several locations in the digestive system, namely the pyloric antrum, the duodenum and the pancreatic islets.[10]

Somatostatin released in the pyloric antrum travels via the portal venous system to the heart, then enters the systemic circulation to reach the locations where it will exert its inhibitory effects. In addition, somatostatin release from delta cells can act in a paracrine manner.[10]

In the stomach, somatostatin acts directly on the acid-producing parietal cells via a G-protein coupled receptor (which inhibits adenylate cyclase, thus effectively antagonising the stimulatory effect of histamine) to reduce acid secretion.[10] Somatostatin can also indirectly decrease stomach acid production by preventing the release of other hormones, including gastrin and histamine which effectively slows down the digestive process.[citation needed]

Brain

Sst is expressed in interneurons in the telencephalon of the embryonic day 15.5 mouse. Allen Brain Atlases
Sst expression in the adult mouse. Allen Brain Atlases

Somatostatin is produced by neuroendocrine neurons of the ventromedial nucleus of the hypothalamus. These neurons project to the median eminence, where somatostatin is released from neurosecretory nerve endings into the hypothalamohypophysial system through neuron axons. Somatostatin is then carried to the anterior pituitary gland, where it inhibits the secretion of growth hormone from somatotrope cells. The somatostatin neurons in the periventricular nucleus mediate negative feedback effects of growth hormone on its own release; the somatostatin neurons respond to high circulating concentrations of growth hormone and somatomedins by increasing the release of somatostatin, so reducing the rate of secretion of growth hormone.[citation needed]

Somatostatin is also produced by several other populations that project centrally, i.e., to other areas of the brain, and somatostatin receptors are expressed at many different sites in the brain. In particular, populations of somatostatin neurons occur in the arcuate nucleus,[11] the hippocampus,[12] and the brainstem nucleus of the solitary tract.[citation needed]

Functions

D cell is visible at upper right, and somatostatin is represented by middle arrow pointing left

Somatostatin is classified as an inhibitory hormone,[3] and is induced by low pH.[citation needed] Its actions are spread to different parts of the body. Somatostatin release is inhibited by the Vagus nerve.[13]

Anterior pituitary

In the anterior pituitary gland, the effects of somatostatin are:

Gastrointestinal system

  • Somatostatin is homologous with cortistatin (see somatostatin family) and suppresses the release of gastrointestinal hormones
  • Decreases the rate of gastric emptying, and reduces smooth muscle contractions and blood flow within the intestine[14]
  • Suppresses the release of pancreatic hormones
    • Somatostatin release is triggered by the beta cell peptide urocortin3 (Ucn3) to inhibit insulin release.[16][17]
    • Inhibits the release of glucagon[16][2]
  • Suppresses the exocrine secretory action of the pancreas

Synthetic substitutes

Octreotide (brand name Sandostatin, Novartis Pharmaceuticals) is an octapeptide that mimics natural somatostatin pharmacologically, though is a more potent inhibitor of growth hormone, glucagon, and insulin than the natural hormone, and has a much longer half-life (about 90 minutes, compared to 2–3 minutes for somatostatin). Since it is absorbed poorly from the gut, it is administered parenterally (subcutaneously, intramuscularly, or intravenously). It is indicated for symptomatic treatment of carcinoid syndrome and acromegaly.[18][19] It is also finding increased use in polycystic diseases of the liver and kidney.

Lanreotide (Somatuline, Ipsen Pharmaceuticals) is a medication used in the management of acromegaly and symptoms caused by neuroendocrine tumors, most notably carcinoid syndrome. It is a long-acting analog of somatostatin, like octreotide. It is available in several countries, including the United Kingdom, Australia, and Canada, and was approved for sale in the United States by the Food and Drug Administration on August 30, 2007.

Pasireotide, sold under the brand name Signifor, is an orphan drug approved in the United States and the European Union for the treatment of Cushing's disease in patients who fail or are ineligible for surgical therapy. It was developed by Novartis. Pasireotide is somatostatin analog with a 40-fold increased affinity to somatostatin receptor 5 compared to other somatostatin analogs.

Evolutionary history

Six somatostatin genes have been discovered in vertebrates. The current proposed history as to how these six genes arose is based on the three whole-genome duplication events that took place in vertebrate evolution along with local duplications in teleost fish. An ancestral somatostatin gene was duplicated during the first whole-genome duplication event (1R) to create SS1 and SS2. These two genes were duplicated during the second whole-genome duplication event (2R) to create four new somatostatin genes:SS1, SS2, SS3, and one gene that was lost during the evolution of vertebrates. Tetrapods retained SS1 (also known as SS-14 and SS-28) and SS2 (also known as cortistatin) after the split in the Sarcopterygii and Actinopterygii lineage split. In teleost fish, SS1, SS2, and SS3 were duplicated during the third whole-genome duplication event (3R) to create SS1, SS2, SS4, SS5, and two genes that were lost during the evolution of teleost fish. SS1 and SS2 went through local duplications to give rise to SS6 and SS3.[5]

See also

References

  1. ↑ "somatostatin". Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc., 2016. Web. 04 mag. 2016 <http://www.britannica.com/science/somatostatin>.
  2. ↑ 2.0 2.1 Lehninger Principles of Biochemistry (8 ed.). Austin. 2021. ISBN 978-1-319-22800-2. OCLC 1243000176. https://www.worldcat.org/oclc/1243000176. "The binding of somatostatin to its receptor in the pancreas leads to activation of an inhibitory G protein, or Gi, structurally homologous to Gs, that inhibits adenylyl cyclase and lowers [cAMP]. In this way, somatostatin inhibits the secretion of several hormones, including glucagon" 
  3. ↑ 3.0 3.1 "Sect. 5, Ch. 4: Structure, Synthesis, and Secretion of Somatostatin". Endocrinology: The Endocrine Pancreas. Medical College of Georgia. pp. 16. http://www.lib.mcg.edu/edu/eshuphysio/program/section5/5ch4/s5ch4_16.htm. 
  4. ↑ "somatostatin preproprotein [Homo sapiens"]. NCBI Reference Sequence. National Center for Biotechnology Information Support Center (NCBI). https://www.ncbi.nlm.nih.gov/protein/NP_001039. 
  5. ↑ 5.0 5.1 5.2 "The evolution of somatostatin in vertebrates". Gene 463 (1–2): 21–8. September 2010. doi:10.1016/j.gene.2010.04.016. PMID 20472043. 
  6. ↑ "Somatostatin and its receptors from fish to mammals". Annals of the New York Academy of Sciences 1200 (1): 43–52. July 2010. doi:10.1111/j.1749-6632.2010.05511.x. PMID 20633132. Bibcode: 2010NYASA1200...43G. https://zenodo.org/record/1450988. 
  7. ↑ "Entrez Gene: Somatostatin". https://www.ncbi.nlm.nih.gov/sites/entrez?db=gene&cmd=retrieve&list_uids=6750. 
  8. ↑ "Human somatostatin I: sequence of the cDNA". Proceedings of the National Academy of Sciences of the United States of America 79 (15): 4575–9. August 1982. doi:10.1073/pnas.79.15.4575. PMID 6126875. Bibcode: 1982PNAS...79.4575S. 
  9. ↑ "Sequence of the human somatostatin I gene". Science 224 (4645): 168–71. April 1984. doi:10.1126/science.6142531. PMID 6142531. Bibcode: 1984Sci...224..168S. 
  10. ↑ 10.0 10.1 10.2 Boron, Walter F.; Boulpaep, Emile L. (2012). Medical Physiology (2nd ed.). Philadelphia, PA: Elsevier. ISBN 9781437717532. 
  11. ↑ Minami, Shiro; Kamegai, Jun; Sugihara, Hitoshi; Suzuki, Nobuchika; Wakabayashi, Ichiji (1998). "Growth Hormone Inhibits Its Own Secretion by Acting on the Hypothalamus through Its Receptors on Neuropeptide Y Neurons in the Arcuate Nucleus and Somatostatin Neurons in the Periventricular Nucleus". Endocrine Journal 45: S19-26. doi:10.1507/endocrj.45.Suppl_S19. PMID 9790225. https://www.jstage.jst.go.jp/article/endocrj1993/45/Suppl/45_Suppl_S19/_pdf. Retrieved 10 January 2021. 
  12. ↑ Stefanelli, Thomas; Bertollini, Cristina; Lüscher, Christian; Muller, Dominique; Mendez, Pablo (February 2016). "Hippocampal Somatostatin Interneurons Control the Size of Neuronal Memory Ensembles". Neuron 89 (5): 1074–1085. doi:10.1016/j.neuron.2016.01.024. PMID 26875623. 
  13. ↑ "Vagal control of the release of somatostatin, vasoactive intestinal polypeptide, gastrin-releasing peptide, and HCl from porcine non-antral stomach". Scandinavian Journal of Gastroenterology 27 (8): 677–85. August 1992. doi:10.3109/00365529209000139. PMID 1359631. 
  14. ↑ 14.0 14.1 Bowen R (2002-12-14). "Somatostatin". Biomedical Hypertextbooks. Colorado State University. http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/somatostatin.html. 
  15. ↑ First Aid for the USMLE Step 1, 2010. Page 286.
  16. ↑ 16.0 16.1 Costoff A. "Sect. 5, Ch. 4: Structure, Synthesis, and Secretion of Somatostatin". Endocrinology: The Endocrine Pancreas. Medical College of Georgia. pp. 17. http://www.lib.mcg.edu/edu/eshuphysio/program/section5/5ch4/s5ch4_17.htm. 
  17. ↑ "Urocortin3 mediates somatostatin-dependent negative feedback control of insulin secretion". Nature Medicine 21 (7): 769–76. July 2015. doi:10.1038/nm.3872. PMID 26076035. 
  18. ↑ "Carcinoid Tumors and Syndrome". https://www.lecturio.com/concepts/carcinoid-tumors-and-syndrome/. 
  19. ↑ "Acromegaly". April 2012. https://www.niddk.nih.gov/health-information/health-topics/endocrine/acromegaly/Pages/fact-sheet.aspx. 

Further reading

External links



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